1. Field of the Invention
This invention relates to buildings made of hollow “logs,” and more particularly to a novel and highly effective combination of elements that greatly improves the strength, thermal and/or acoustical insulation, and other properties of such buildings while reducing their cost.
2. Description of the Prior Art
Hollow logs enclose an air chamber and therefore have a thermal insulation capacity. But if hollow logs are assembled to form a wall or roof and are made of certain materials, like steel, such capacity is limited, because there is no thermal convection barrier between the logs and because logs made of those materials readily conduct heat from the warmer side to the cooler side of the wall or roof. In view of the high price of oil and other fuels, these aspects of the system are worth reconsidering. As indicated below, the applicant has addressed this handicap by closing the interstices between the logs in a novel way.
Log buildings have a long history, as indicated in applicant's co-pending U.S. patent application Ser. Nos. 12/157,051 and 12/218,913, filed respectively on Jun. 6 and Jul. 18, 2008. Those applications and the applicant's prior U.S. Pat. Nos. 4,619,089 and 5,282,343 are incorporated herein by reference. Traditional log buildings made of wood have drawbacks, including the sheer weight and bulk of the logs and the consequent expense and difficulty of shipping and handling them; their lack of uniformity, even when trimmed to size; the inevitable waste, and, in many locales, the scarcity of wood. But because log structures have a certain aesthetic appeal, wood logs are still used to some extent to construct houses, sheds and other low-rise buildings including apartments, schools, lodges and commercial buildings. Usually, however, wooden structures today are not made of logs but are framed with sills, joists, studs, rafters, and ridgepoles and finished with interior and exterior sheathing.
As applicant's co-pending applications identified above explain, the construction of log buildings has undergone considerable evolution. Whereas it traditionally employed solid wood logs, it now may employ hollow metallic “logs” that have undeniable merits, including savings in the cost and volume of materials, shipping and labor, lack of dependence on skilled labor, speed of construction, adaptability to use in remote locations, and resistance to damage by fire and termites. Indeed, experts predict that hollow metal structures called “metalogs” by analogy to conventional wood logs could become a preferred way of construction in much of the world for low-rise buildings.
The '089 and '343 patents identified above and corresponding patents in other countries disclose the best prior examples of metalog construction. Buildings following their teachings have been erected in many parts of the world and are finding wide and growing acceptance. They are suitable for all markets in view of their properties noted above. Government authorities and private builders in various countries have endorsed them because of their affordability and the rapidity with which they can be erected, etc.
Air is a poor conductor of heat and in the absence of convection a good insulator. One reason for the growing popularity of hollow-metal-log construction is that metalogs, by virtue of the air they enclose, have inherent insulating properties, even if made of a material such as aluminum or steel that readily conducts heat. In some climates, however, their inherent insulating properties may be insufficient, since the metal, even though thin and thus having relatively modest mass, conducts heat from the warmer side of a wall formed by the logs to the cooler side. (We sometimes also say colloquially that “cold”—the absence of heat—is conducted from the cooler side of the wall to the warmer side.) Even if the logs are made of plastic or another material having good insulating properties, conventional hollow log structures may not be suited to extreme climates.
In cold climates, the conduction of heat through the material of which the logs of an exterior wall are formed and the radiation of the heat into the surroundings cools the material and therefore the air within the building near the wall. This increases the density of that air and causes an uncomfortable downdraft of cold air near the wall, and an uncomfortable flow of cold air near the floor and towards the center of the room of which the wall forms a boundary. Below a certain temperature that depends on the relative humidity of the air within the room, condensation forms on the wall, giving the room a clammy feeling. And the constant escape of heat to the environment increases the expense of maintaining a set temperature within the building. The high and rising price of heating oil and other fuels intensifies the need to find a remedy.
In hot climates, the flow of heat is often in the other direction. Solar radiation heats the outer side of the logs, and the material of which the logs are made conducts the heat to the interior of the building, raising the temperature and causing discomfort to the people there. Even after sunset, it is likely in the absence of air-conditioning to be noticeably warmer inside than outside the building. And the operating cost of air-conditioning is proportional to the ease with which heat flows from the outside to the inside of the building.
Thermal insulation is of course known as a means of helping to control temperatures in structures of all types in both cold and hot climates. An installation of thermal insulation in a conventional wood-frame structure involves blowing insulating material into the spaces between studs, joists or rafters, and/or positioning batts or mats of insulation by hand in those spaces. As conventionally practiced, both methods have a number of drawbacks.
In either case, the thickness of the insulation is often determined by the width of the studs, joists or rafters, rather than by the required R-value (apparent thermal conductivity) of the insulation.
Batt and mat insulation has the additional drawback that it is likely to leave small gaps between the batts or mats and adjoining support structures, thereby providing passages for the escape of heat. Since the adjoining support structures such as two-by-four studs are normally at intervals of 16 inches in the US and at similar intervals in other countries, there may be many such leakage passages in the span of a typical wall or roof.
Blown insulation poses a significant health risk to the workers who do the installation. Inevitably, despite wearing (usually nowadays, though not formerly) protective masks, they inhale small airborne fibers of asbestos, rock wool, fiberglass or other insulating material, which can cause mesothelioma, chronic obstructive pulmonary disease and other serious medical conditions.
Neither blown insulation nor manually placed batts or mats have been used in hollow-metal-log construction. Insulation blown into hollow metal logs would have indeed a benefit, but the net benefit would be modest, because blown insulation displaces air—itself a good insulator—and does little to retard heat transfer through spaces between logs by convection or through the metal by conduction. And neither blown insulation nor batts/mats can be deployed in separate channels exterior to hollow metal logs without the provision of elaborate auxiliary structure for their support or, at least, their protection from weather, etc.
Applicant's '343 patent identified above discloses in FIGS. 8a-d and associated text the best methods known heretofore of applying thermal insulation to metal logs. They involve winding a mat through gaps between logs, covering the logs with wide mats overlapping like shingles on one or both sides of the logs, or wrapping mats around the logs to form sleeves. None of these methods provides structural support for a wall or roof or provides weather resistance, and all require additional interior and exterior sheathing.
In conventional metal log construction of, say, a rectangular wall, hollow metalogs, each extending usually horizontally, are arranged in adjacent, parallel, superposed relation. The logs are supported at their ends, typically though not necessarily in slightly spaced-apart relation, by end connectors each having a connecting portion inserted into a log and a stackable portion. The stackable portions are stacked one above another. Alternatively, the ends of the logs are stacked in vertical retaining grooves formed in stanchions, as shown in FIGS. 12 and 13 of the applicant's '089 patent mentioned above.
In conventional practice, in order to prevent infiltration of air and water, it is necessary to install at least exterior sheathing, and builders usually wish to install interior sheathing as well.